In the prior art numerous assembly processes for electronic systems adapted to large-scale production are diffused. Basically, every assembly process involves mounting one or more electronic devices on an electronic board (for example, a Printed Circuit Board or PCB). Generally, any electronic device comprises one (or more) chip of semiconductor material on which an electronic component (or an electronic microcircuit) is integrated. The chip is encapsulated in a package of insulating material to be isolated and protected from the external environment. The package exposes conductive pins, which are coupled to corresponding terminals of the conductive chip. The pins of the package are soldered to the conducting tracks formed on the electronic board. This allows the interaction between the electronic component, encapsulated in the package, and other electronic devices mounted on the electronic board in a similar way, through the conducting tracks properly connected to each other.
The soldering between the pins of electronic devices and tracks the electronic board should be performed homogenously to ensure proper operation and/or performance of the electronic system. At the same time, the soldering should ensure a stable mechanical connection between the electronic devices and the electronic board.
For example, a known soldering technique is the wave soldering technique. In this case, the electronic devices are initially glued on the electronic board by means of an adhesive paste, so that the pins of the electronic device correspond to soldering areas on the electronic board. Subsequently, the assembly thus obtained is placed over a bath of molten soldering paste, with a gluing surface of the electronic board (on which electronic devices are glued) facing downward. The assembly is then flooded with a wave of molten soldering paste, which laps the electronic board so as to bind to the soldering areas of the electronic board soldering the pins of electronic devices. In this way, the electronic devices are mechanically and electrically coupled to the electronic board.
The wave soldering technique described above, however, may be problematic with certain types of electronic devices. For example, this may occur in the case of Surface-Mounting Technology (SMT) electronic devices having, instead of pins protruding from the package, pins consisting of areas of exposed metal on a mounting surface of the package of the electronic device on the electronic board—devices known in the art as “No-Lead” or “Micro-Lead”—especially if small sized.
In fact, a gap that is formed after the gluing of the package, between the pins of these “No-Lead” or “Micro-Lead” devices and the soldering areas may be too narrow for allowing the wave of soldering paste to enter therein in an optimal way—in particular, in the case of pins with a relatively extended surface. Moreover, it may happen that, after the gluing, the electronic devices result positioned with the mounting surface not perfectly parallel to the electronic board due to a reduced number and/or a sub-optimal allocation of disposition sites at which the most common adhesive pastes are dispensed on the mounting surface of the electronic devices. Furthermore, the scaling of the electronic device accordingly reduces its mounting surface, while the size of the pins remain essentially unchanged to ensure the same current density delivered by the device, thereby reducing the available space on the mounting surface for the gluing points—for example, space for gluing points may not be available in some locations at the perimeter of the mounting surface. Therefore, due to the imperfect positioning of the electronic devices on the electronic board, during wave-soldering the soldering paste may be distributed not homogenously. For these reasons, it may happen that the coupling between the pins and soldering areas of the card is not satisfactory or is not achieved at all. The electronic system so assembled would have both performance and a useful life lower than expected, up to the limit being completely broken.